Date of Thesis



Previous studies have revealed that non-human primates discriminate quantities. However, their performance is highly variable both within and between species. Discrepancies in performance may be the result of a variety of factors, including species-specific cognitive differences or task specific factors such as representational format of the choice stimuli, motivation to perform that task, or tolerance for task delays. Six brown capuchin monkeys (Cebus apella) and six squirrel monkeys (Saimiri sciureus) were presented with two numerical quantities in three different conditions, replicating Schmitt and Fischer's (2011) study with baboons and macaques. Primates were rewarded with a quantity of food corresponding in number to the quantity of the choice stimulus selected. Results revealed an influence of representational format and species on performance, however, other potential confounding variables remained that may have been affecting performance. Additional testing of the influence of the motivational value of the food reward and the time delay between choice and reward revealed a significant effect of motivation on performance. Increasing the motivation resulted in the lack of an effect of both modality and species on quantity discrimination performance. These results suggest that poor performance in quantity discrimination tasks can be potentially explained by a lack of motivation to perform.


capuchins, squirrel monkeys, modality, counting, motivation

Access Type

Honors Thesis

Degree Type

Bachelor of Science


Animal Behavior

First Advisor

Reggie Gazes

Second Advisor

Peter Judge